Dynamometer excitation control system



Dec. 7,1943. I R. H.-KAUFMANN 2,335,860

DYNAMOMETER EXCITATION CONTROL SYSTEM Filed Sept. 4, 1940 o DYNAMOHETER EXCITATION SPEED I nventor: Richard H. Kau fmann,

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His ttorney.

Patented Dec. 7, 1943 DYNAMOMETER EXCITATION CONTROL SYSTEM Richard H. Kaufmann, Schenectady, N. Y., assi'gnor to General Electric Company, a corporation of New York Application September 4, 1940, Serial No. 355,321

11 Claims. (CI. 73-51) This invention relates to an electrical dynamometer and particularly to an electrical dynamometer which is adapted to impose a load of certain characteristics upon a power source such as an internal combustion engine.

It is an object of my invention to provide an improved dynamometer excitation control system.

It is another object of my invention to provide an excitation control system for a dynamometer employed for loading a mechanical power source whereby the actual operating characteristics of the power source ma be duplicated by causing the power absorbing means to have a definite and predetermined relationship to its speed.

It is a further object of my'invention to provide an improved dynamometer excitation control system in which the total dynamometer excitation is functionally related to the speed and whichmay have components which vary as the firstor second power of the speed or assume intermediate values of total excitation between these two limits.

Other and further objects and advantages of my invention will become apparent as the description proceeds.

In order to simulate in the laboratory the conditions of actual service with various types of loads, for example, propellers driven by an internal combustionengine, it is desirable to pro-' vide and excitation system for a dynamometer employed in loading the prime mover or engine which automatically will maintain with varying loads the desired power-speed relationship. In carrying out my invention in its preferred form, a pair of direct current generators which are driven at a speed proportional to the dynamometer are adapted to be employed for exciting the dynamometer field. One of these exciters has. its armature connected to the field of the dynamometer while its field is connected in circuit with the armature of the other exciter generator and with an adjustable source of voltage. The other exciter may be excited either from an adjustable voltage source of supply or by means of a permanent magnet, the former being the preferred arrangement on account of flexibility and the ability to avoid excessive voltages. The exciter whose armature is connected for energizing the dynamometer field is operated preferably in the unsaturated condition. By adjusting the relative magnitudeof the adjustable and variable components of excitation supplied to the field of the exciter which supplies the dynamometer field, the horsepower absorption of the dynamometer as a function of speed may be made to vary automatically over a wide range. Further, by providing suitable switching means the dynamometer may be supplied with excitation in dependent of variations in speed.

In a modification, the output of the exciter,'

which in the foregoing arrangement is connected directly to the dynamometer field, is connected to the input of a dynamo-electric amplifier instead of being directly connected to, the dynamometer in the appended claims. My invention, however,

both as to its organization and its method of operation will be better understood with refervence to the following description when considered in connection with the accompanying drawing in which Fig. 1 is a schematic electric circuit diagram of apparatus arranged in accordance with my invention; Fig. 2 is a'modification of the arrangement of Fig. 1; and Fig. 3 illustrates several characteristic curves which will be employed in explaining my invention.

Referring to Fig. 1 of the drawing, the numeral I I represents a prime mover in the form 01 an internal combustion engine having a throttle l2 and mechanically connected by means-oi a rotary shaft 13 to the rotor ll of a dynamometer ii, for example, of the inductor eddy current type. Connected also to the shaft I! or arranged to be driven at a speed proportional thereto are the rotors or armatures l8 and ll of a pair of direct current exciter generators l8 and IS. The dynamometer I5 is provided with a field winding 20 which is adapted to be excited from the armature ll of the exciter generator l9 through a three position double-pole switch 2! and controlled by a pair of rheostats 22 and 23, the rheostat 22 being the main control memher and the rheostat 23 being a vemler element. By throwing the switch 2| to the right, the dynamometer field 20 may be connected to a constant voltage source of supply 24. .The rheostats 22 and 23, under either condition of operation, serve to control the actu 1 amount of load or excitation where manual control is employed to obtain the exact load setting. The exciter generator i9 is preferably designed to operate on the straight portion of its saturation curve.

When the switch 2! is in the intermediate po-v sition as illustrated in the drawing, the dynamometer field 20 is excited'from a plurality of series-connected independent voltage sources, one

beingthe armature I I of the exciter I 9 and the other the constant voltage source 24. A potentiometer type rheostat 24a having an adjustable contact 24b provides means for deriving adjustable amounts of the constant voltagecomponent. The exciter generator I9 is provided with the usual field winding 25 which is shown connected to the armatureli or the smaller pilot exciter generator I8 through a potentiometer type rheostat 26 anda Vernier rheostat 21. The potentiometer 26 is connected to the constant voltage source of supply 24 and is arranged so that the voltage across it adds to that of the armature I6 of the pilot exciter I8. By means of an adjustable contact 28 different values of voltage may be derived from the potentiometer 26.

The exciter generator I8 is provided with a generators in a manner to ascertain their load requirements.

field Winding 29 which is supplied with direct current from the separate source 24-. A suitable arrangement such as a rheostat 30 provides means for supplying the field 28 with any desired uniform excitation. By means of a switch 3| the field winding 29 may be disconnected from the source of supply 24.

The dynamometer I5 may be provided with the customary scale beam to form a conventional cradle type dynamometer. It will also be appreciated that other types of dynamometers may be employed in carrying out the principles of my invention together with other means of measuring the power absorbed. v

.The arrangement of Fig. 2 is disclosed in a divisional application, Serial No. 474,479, filed February 2, 1943, and assigned to the assignee of this application and is quite similar to that of Fig. 1 but has several points of distinction. One point of distinction-resides in the insertion of an amplifier 34 between the armature I1 oi the exciter I9 and the field winding of the dynamometer. In the illustrated embodiment I have shown an amplifier of the dynamoelectric type comprising a conventional direct current generator which is preferably designed to operate on the straight portion of its saturation curve and which includes an armature 35 and 'a field winding 36. The amplifier 84 also comprises a suitable constant speed motor 31 preferably of the synchronous or induction type for driving the armature 85. Since the direct current generator is operated in the unsaturated condition and has its armature 35 drivenat a constant speed, it delivers a voltage to the dynamometer field 20 which is proportional to the excitation which is supplied to its field or input circuit 36. This generator may be replaced by a direct current machine of the armature-reaction excited type, such for example as that disclosed and claimed in Patent No. 2,227,992, E. F. W. Alexanderson and M. A. Edwards, granted January '7, 1941, and which is assigned to the assignee of the present invention. Furthermore, an electronic amplifiemnay be employed in lieu of the dynamoelectric type, if desired. 1 7

As indicated previously, the pilot exciters I8 and I2 oi the foregoing arrangement may or may not be cradled, with the dynamometer depending upon the required size of the exciter generator.

Another point of difference in the arrangement of Fig. 2 over that of Fig. 1 resides in the substitution of a potentiometer type rheostat 38 for the series rheostat 22 in the dynamometer provided. The field winding b is connected I to the armature I6 of the pilot exciter generator I8 through a switch 42 for deriving a voltage component of excitation which is variable with the speed. The arrangement of Fig.- 2 differs 20 further from that of Fig. 1 in that thefield winding 29 of the smaller pilot exciter generator I8 is shown connected to the source of supply 24 through a potentiometer type rheostat 4| and a vernier element 40. With thislatter arrange- 25 ment the voltage applied to field winding 29 30 field winding 20a in addition to the winding 20.

These windings 'are connected to produce magnetic fluxes in the dynamometer which are inthe same relative direction. The field winding 28a is connected to the constant voltage source 24 through the potentiometer 24a for supplying the constant component of excitation when the dynamometer excitation is being obtained from two independent voltage sources. It will be appreciated, however, that the arrangements of-Figs. l

4 and 2 may be used alternatively so far as this feature is concerned. p

In operation, assume that the switch 2| is thrown to the left position to connect the armature I! of the exciter I8 in circuit with the field winding 28 and the rheostat 22 and 23 of Fig. 1, or in circuit with the input winding 36 and the potentiometer 38 of Fig. 2. The first exciter I8 receives its excitation from the constant direct current source 24 and this excitation may be adjusted by the series rheostat 38 of Fig. 1 or the rheostats 4| and 40 of Fig. 2. The second exciter generator I9 receives its excitation from the When these pilot exciter generators are of such A small size in comparison to the size or the dyna-' mometer that the torque required to drive them is negligible these units need not be cradled. Hencaby the employment of an amplifier such armature I6 of the first exciter I8 and from the constant voltage source of supp y 24 through the potentiometer'26. The excitation component delivered to the exciter I9 from the exciter I8 increases proportionally to the speed of the exciter I8 since the latter has constant excitation applied to its field. The component of excitation supplied to the winding 25 or to the winding 25 1. from the potentiometer 26, however, is independent of the speed.

Since exciter-generator I9 is also driven at' a speed proportional .to that Ofgthe dynamometer,

' arise with the speed, the voltage output at the as 34 for the output of exciter I9, 1 pilot on citers may b used and thereby avoid the ex= pause and inconvenience oi mounting the exciter '35- armature II oithe exciter generator increases more rapidly. It will be seen that the exciter generator ighaa a component of voltage in its ature circuit which varies directly as the speed due to the excitation supplied from the potentiometer 28, and if the exciter l9, as in the instant case, is designed so that it operates in the unsaturated condition or on the straight portion of its saturation curve the output voltage com- 5 ponent due to the excitation received from the exciter generator I8 will then increase approximately as the square of the dynamometer and exciter generator speed. This follows from the fact that the generated voltage in the ,armature 10 |3 as a voltage which varies as the square of the speed. As indicated heretofore, in the apparatus disclosed .in Fig. 1, this armature voltage is applied to the field of the dynamometer directly through the rheostat 22 and 23, while in the apparatus illustrated in Fig. 2, the voltage 20 from the exciter I9 is connected to the input circuit of the linear response amplifier 34, the out-, put of the amplifier being connected to the dynamometer field 20.

In order more fully to explain the operation 25 and manner of adjustment of the system, Fig. 3

has been presented to show typical curves of the excitation supplied to the field winding 20 ob-, tained with my improved excitation system.

These curves have been drawn to show the generai relationships obtainable between the dynamometer excitation and the speed. lhe curve 0A represents the dynamometer excitation characteristic which is obtained by the use of only the constant voltagecomponent of excitation in the arrangement of Fig. 2, the voltage supplied to the field winding 29 may be reduced to zero by adjusting the adjustable contact of the potentiometer 4|. For such a condition of operation the excitation of the-dynamometer is caused to vary linearly with the speed thereby producing a corresponding change in the dynamometer torque. The rate of rise of excitation with speed may be controlled by the potentiometer contact 28. The curve OB represents the type of excitation characteristic obtainable without any fixed component of excitation applied to the field of,

the exciter i8. In both of the arrangements of Figs. 1 and 2, this may be accomplished by adlusting the movable contact 28 of the potentiometer 28 so that-the voltage obtained from the at low speeds.

source of supply 24 is zero. In this case the dynamometer excitation isvaried in accordance with the square of the speed to produce corresponding changes in the dynamometer torque.

The characteristic 00 represents the combined excitation characteristic obtainable when both of the excitation sources for the field winding 25 are in operation. It is clear that, with the field adjusting elements of the exciter generators l8 and I9 set to a given position, the magnitude of 5 the excitation current supplied to the dynamometer field 20 may be adjusted by means .of the rheostats 22 and 23 of Fig. l andthe potentiometer 3B and the vernier rheostat 23 of Fig. 2.

By proper adjustment of the exciter field control elements, the relative magnitudes or proportions of the two excitation components supplied to the dynamometer for a given .speed or speeds may be altered as desired to impose horsepower loads on the engine which vary automatically as a function of speed in the desired manner. For example, by'increasing the resistance in rheostat 30 of Fig. 1, or by moving the contact arm of potentiometer ll of Fig. 2 to the left, to reduce the voltage applied to the field 29 of exciter II, the rate of rise or the magnitude of the voltage component for excitingthe dynamometer field which varies as the square of the speed is reduced. By

moving the arm 22- of the potentiometer 26 to the left, the magnitude of the dynamometer excitation voltage component which varies as the first power of the speed is reduced. The ease with which the overall characteristic curve can be altered by the simple adjustment of two rheostats is a most valuable feature.

In describing the operation of the arrangement of Figs. 1 and 2, the switch 2| was assumed to be thrown to the left to connect the dynamometer field 20 with the armature ll of exciter I! for automatic operation. At times it may be desirable to use manual control and eliminate the effect of the automatic excitation completely, that is, to secure excitation for the dynamometer which is independent of speed changes. For such operation the switch 2| is thrown to the right to connect the exciting field winding 20 of the dynamometer in Fig. 1, or the input'circuit 35 of the amplifier in Fig. 2, to the constant voltage direct current source of supply 24 and in this way the system operates with conventional constant excitation which can be adjusted by rheostats 22 and 23 of Fig. 1, or by the potentiometer and vernier of Fig. 2, to obtain the desired load. In the arrangement of Fig. 2, all or a portion of this constant excitation may also be provided by means of the field winding 20a.

When it is desired to operate the system by supplying a constant component of excitation to l the dynamometer in conjunction with the component or components which are functionally related to the speed, the switch 2| of Fig. 1 is maintained in the intermediate position to connect the armature I1 in series additive relation with the constant voltage source 24'. For this same condition of operation, in the systein of Fig. 2, the switch 2| is thrown to the left and the constant component of excitation is supplied to the field winding 20a through the rheostat 24a in such a manner that both voltages cause magnetic fluxes to be produced in the dynamometer in'the same relative direction. This connection also serves the additional purpose of permitting maximum excitation at any speed down tczero on the dynamometer thereby permitting maximum available torque to be obtained on the dynamometer even I have thus provided an improved excitation system which is capable of delivering a voltage which is independent of speed for exciting the dynamometer field. I havealso provided an arrangement whereby the dynamometer excitation may be varied directly as the speed thereb producing a modified shape in the horsepower-speed characteristic of the dynamometer. Further, I may obtain a dynamometer excitation characteristic which is appfoximately proportional to the square of the speed in order to produce a change in the horsepower-speed characteristic such that the horsepower absorption increases at a faster rate with respect to speed. Also, by combining in additive relation the excitation component for themain exciter generator l8 which is independent of the speed with the ccm-' ponent of excitation which varies with the speed.

may be made automatically to vary in accordance with the firstpower oi the speed and over a range including the second power with the result that the horsepower absorption 01' the dyna- .mometer as a function of speed may be made to assume intermediate values.

I have also provided means whereby a constant component of excitation may be supplied simultaneously to the dynamometer with the bilizing action to prevent huntingor overspeed- ,ing by producting a pronounced increase in the jdynamometer torque with increases in speed in those; cases where the dynamometer would have a jfiat or nearly uniiorm-speed-torque characteristic over a large part of its speed range if the excitationwere held at a constant value.

The apparatus is thus adapted for producing in the laboratory various torque-speed and horsepower-speed relationships for simulating diflerent types of loads sothat operating characteristics similar to-that found in actual practice from the standpoint of stability and con- .trol may be obtained. The apparatus is particularly useful in those cases, where the excitation and torque of the dynamometer are not related in a simple manner. In other words, in order to obtain an absorption torque, for example, which varies as the square of the speed, it may be necessary to increase the field excitation at a different rate. A1so,-due to difierences in various machine designs, this rate or the relative curvature of the total required dynamometer excitation curve changes for different machines. This difference in excitation rate is readily obtainable by changing the proportions or relative magnitudes of the various excitation components.

In accordance with the provisions of the patent statutes, I have described the principle of operation or my invention together with the apparatus which I now consider to represent the best embodiment thereof but I desire to have it understood that the apparatus shown is merely illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters-Patent of the United States is:

1. In combination in a system for testing prime movers, an electric dynamometer com-. prising a field exciting winding and a rotary element adapted to be coupled to the prime mover to be tested for placing a load of controllable speed-horsepower characteristics on said prime mover, a direct current generator having a'field exciting winding and an armature drivenat a speed proportional to the dynamometer, means tor exciting said dynamometer field exciting winding in proportion to the armature voltaso variations of said generator, and apluralityioi Y independent voltage sources for exciting the field 1 exciting winding of said generator, the voltage obtained from one of said voltage sourceabeing variable in accordance with the speed tame dynamometer, the voltage obtained irom the other of said voltagesources being indepe'ndeet 2. In combination in a device for testing prime movers, an electric dynamometer including a rotary element adapted to be mechanically connected to the prime mover to be tested, said dynamometer also including means for controlling its speed-torque characteristics, a generator having a field exciting winding and an armature driven at a speed proportional to the dynamometer, means connecting said dynamometer com trol means for energization in accordance with the armature voltage variations of said genera tor, a plurality ofindependent voltage sources, means for exciting the field exciting winding of said generator from said voltage sources,- the voltage obtained from one of said voltage sources being variable in acordance with the speed of said dynamometer, and means for varying the ratio of the voltages derived from said voltage sources corresponding to a given speed.

3. In combination in a testing device, an electric dynamometer including a rotary element and an operating winding for controlling the absorption capacity of saiddynamometer, said rotary element being adapted to be driven by a mechanical power producing member to be tested, a generator having a field winding and an armature member driven at a speed propor-, tional tothe dynamometer, and means comprising a plurality of independent voltage sources connected in series relation with each other for supplying current to the field winding of said generator and themagnitude of a component of field current from one of said-voltage sources varying with the speed of said dynamometer, and

means for energizing the operating winding of I said dynamometer in proportion to the voltage -variations in the armature-of said generator.

- 4. In combination in a testing device, an electric dynamometer including a rotary element and 40 an operating winding for controlling the absorption capacity of said dynamometer, said rotary element being adapted to be driven by a power producing member to be tested, a generator having a field'winding and an armature element driven at a speed proportional to the-dynamometer, means electrically connecting the operating winding of said dynamometer to be energized in accordance with voltage variations in the armature of said generator, means comprising a plurality of independent voltage sources connectedin series relation with each other for supplying current to the field winding of said generator,

one of said voltage sources producing a voltage which varies in accordance with the speed of said dynamometer and the voltage derived from said other voltage source being adjustable in magnitude, whereby the torque of said dynamometer may be made to vary in proportion to values 'io windingfoi said dynamometer in accordance with the voltage variations in the armature or said exerator, a second excitergenerator comarmature and magnetic fi'eldproducmeans, the armature or'saidsecond exciter 7:; generator being driven at a speed proportional to said dynamometer for changing automatically the torque absorbing capacity 01' said dynamometer in accordance with variations in speed, the

voltage derived from said constant voltage source being adjustable in magnitude for changing that component of exciter excitation which is independent of the speed.

6. In combination, an electric dynamometer for placing a load of controllable speed-torque characteristics on a mechanical power source, said dynamometer including a rotary element adapted to be connected to said mechanical power source, said dynamometer also including a field winding, a first exciter generator driven at a speed proportional to said dynamometer, said first exciter generator comprising an armature and a field winding, means connecting the armature of said first exciter generator for exciting said dynamometer field winding, a second exciter generator having a field winding and an armature member driven at a speed proportional to said dynamometer, a substantially constant voltage source of supply, means for deriving adjust, able amounts of voltage from said constant voltage source of supply, means connecting the voltage derived i'rom said adjustable means in series additive relation-with the voltage produced in the armature of said second exciter generator for exciting the field of said first exciter generator, and means for varying the exciting current supplied to said second exciter generator field winding, said last named means and said adjustable means providing means for changing the relative magnitudes of said series connected voltages corresponding to a given speed.

'7. In combination, in a testing system, an electric dynamometer for placing a load of controllable speed-torque characteristics on a mechanical power source, said dynamometer comprising a rotary element adapted to be connected to said power source, said dynamometer also including a field winding, a first exciter generator havingan armature driven at a speed proportional to said "dynamometer, a field winding for said first exciter generator, a second exciter generator having a field winding and an armature member driven at a speed proportional to said dynamometer, means for exciting'the field winding of said second exciter generator, a substantially constant voltage source 01' supply, a potentiometer including a movable element for deriving adjustable values of voltage from said source of supply, and

- means connecting the armature of said second exciter generator in series circuit relation with said potentiometer including said movable element for supplying excitation to said first exciter generator field winding, the armature of said second exciter generator being adapted to generate a component of voltage which varies linear- .ly with the speed, said adjustable component of voltage being adjustable over a range starting from zero and said variable component being adjustable over a range starting from substantially zero for'a given speed whereby the slope of the 8. In combination in a device for testing prime movers, an electric dynamometer for loading the prime mover to be tested, said dynamometer having a field winding for controlling the speedtorque characteristics thereof, a first exciter generator having field control means and an armature member driven at-a speed proportional to the dynamometer, means for energizing the field winding of said dynamometer in accordance with thevoltage variations in the armature of said first exciter generator, a second exciter generator having a field winding and an armature member driven at a speed proportional to the dynamome eter, asubstantially constant voltage source of supply, means for deriving voltages of adjustable magnitude from said source oi supply, means connecting the armature of said second exciter generator in series relation with the adjustable dynamometer excitation curve may be changed from a value which varies directly as the speed to e a value which varies substantially as the square of the speed.

voltages derived from said constant voltage source for energizing the field producing means of said first exciter generator, whereby the field producing means of said first exciter generator may be energized in accordance with a component of voltage which varies in accordance with the speed of said dynamometer, variable means for exciting the field winding of said second exciter generator, and means for selectively connecting either the armature of said first exciter generator or said constant voltage source of supply to energize the field winding of said dynamometer, whereby the excitation of said dynamometer may be made to assume a plurality of intermedate values which vary as a function of speed between the limits of the first and the second power of the speed or whereby said excitation may be made independent of speed.

9. In combination in a system for testing prime movers, an electric dynamometer comprising a field exciting winding and a rotary element adapted to be coupled to the prime mover to be tested for placing a load of controllable speedtorque, a direct current generator having a field exciting winding and an armature, driven at a speed proportional to the dynamometer, a substantially constant voltage source of supply, means for exciting said dynamometer field exciting winding in accordance with voltage components derived from the armature of said generator and said constant voltage source of supply, and fa plurality of independent voltage sources for exciting the field exciting winding of said generator, the voltage obtained from one of said voltage sources being variable in accordance with the speed of said dynamometer, and the voltage obtained from the other of said voltage sources being independent of speed.

10. In combination in a testing device, an electric dynamometer including a rotary element and an operating winding for controlling the absorption capacity of said dynamometer, said rotary element being adapted to be driven by a power producing member to be tested, a generator having a field exciting winding and an armature ele, ment driven at a'speed proportional to the dynamometer, a plurality of independent voltage sources connected in series relation with each namometer operating winding, one of said voltage sources comprising the armature of said generator and the other of said voltage sources being independent of speed variations of said dynamometer, and a plurality of voltage sources for exciting said field exciting winding of said generator, the voltage obtained from one of said voltage sources being variable in accordance with the speed of said dynamometer, and the other 0! said voltage sources being independent of said speed.

11. In combination in a system for testing prime movers, an electric dynamomet-er comprising a fleld exciting winding and a rotary element adapted to be coupled to the prime mover to be tested for placing a load of controllable speedtorque characteristics on said prime mover, a direct current generator having a fleld exciting winding and an armature driven at a-speed proportional to the dynamometer, a supply-voltage independent of the speed of said 'dynamometer, means for energizing said dynamometerfleldex citing winding in accordance with voltages obtained from the armature 01' said direct current generator and said independent supply voltage and in a manner whereby said voltages cause said field exciting winding to produce magnetic fluxes in the'same direction, and means foren- -ergizing said generator field exciting winding in accordance with voltages one oi which varies in accordance with the speed of said dynamometerl 

